Refactoring Static Methods

[PujaDeshmukh17]

Describe your changes

Currently all the methods in TokenHandler and DBQuery class are static methods. This is making the code less maintainable and creating issues while writing UTs.
The current PR is intended to change this implementation and make all the static methods in these classes as non static. Also DBQuery and TokenHandler have been implemented using singleton pattern in order to make sure that only single instance of these classes gets created.

Any documentation

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist before requesting a review

• I follow Java Development Guidelines for SAP
• I have tested the functionality on my cloud environment.
• I have provided sufficient automated/ unit tests for the code.
• I have increased or maintained the test coverage.
• I have ran integration tests on my cloud environment.
• I have validated blackduck portal for any vulnerability after my commit.

Upload Screenshots/lists of the scenarios tested

• I have Uploaded Screenshots or added lists of the scenarios tested in description